Polymer electrolyte fuel cell and manufacturing method for electrode-membrane-frame assembly

ABSTRACT

A MEA-frame assembly is arranged in a mold for injection molding to form a first flow passage arranged so as to extend along the outer periphery of an electrode between the outer periphery of the electrode and the inner periphery of a frame, a second flow passage arranged so as to extend along an inner elastic member between the inner periphery and outer periphery of the frame and a plurality of connecting flow passages which communicate the first flow passage with the second flow passage. An elastic resin is injected into the first flow passage to fill the first flow passage with the elastic resin and to fill the second flow passage with the elastic resin through each of the communicating flow passages, thereby an elastic member which hermetically seals the space between the MEA-frame assembly and the separator is integrally formed.

This application is a continuation application of application Ser. No.12/306,986, which is the U.S. national stage of InternationalApplication PCT/JP2008/000758, filed Mar. 27, 2008.

TECHNICAL FIELD

The present invention relates to a solid polymer electrolyte fuel cell,and particularly, to an improvement in the seal structure between anelectrolyte membrane electrode assembly and electroconductive separatorof a fuel cell.

BACKGROUND ART

In conventional solid polymer electrolyte fuel cells, a single cellmodule is used which is constituted by sandwiching a MEA-frame assemblyin which a membrane electrode assembly (MEA) is supported by a frameprovided with a gasket arranged around its periphery for sealing gasbetween an anode side electroconductive separator plate and a cathodeside electroconductive separator plate. The MEA is constituted of apolymer electrolyte membrane, and an anode bound to one side of thispolymer electrolyte membrane and a cathode bound to other side of thepolymer electrolyte membrane. Gas supply sections are formed on theperiphery of each separator plate to supply fuel gas to the anode andoxidizer gas to the cathode of the MEA, respectively.

However, this conventional solid polymer electrolyte fuel cell, as shownby a sectional view of an electrode-membrane-frame assembly in FIG. 15,gives rise to the occurrence of the so-called cross-leak phenomenon inwhich a part of the gas supplied to the inside of the battery isdischarged through this clearance 303 because a clearance 303 is presentbetween the inside periphery of a frame 300 and an electrode (MEA) 302with respect to necessity of the assembly of the frame 300 and aseparator 301.

Further, for improving this phenomenon, there are a proposal of astructure in which, as shown by a sectional view of anelectrode-membrane-frame assembly in FIG. 16, a second gasket 308 isarranged in this clearance 303 and a proposal of a method in which apart of the inside periphery of the gasket is placed to be partially incontact with the outside periphery of the electrode 302 (not shown, seefor example, Patent Document 1).

Further, the MEA, namely, the polymer electrolyte membrane isincorporated into almost the center of the thickness of the frame and asa binding method thereof, a thermal pressure bonding method, methodusing an adhesive and a method using a mechanical cramp are adopted.

Further, as a structure of arrangement of the gasket and the like in theelectrode-membrane-frame assembly, other various structures are proposed(see, for example, Patent Documents 2 to 7).

Patent Document 1: JP-A No. 2005-100970

Patent Document 2: JP-A No. 2006-172752

Patent Document 3: JP-A No. 2006-310288

Patent Document 4: JP-A No. 2001-102072

Patent Document 5: JP-A No. 2005-259465

Patent Document 6: U.S. Pat. No. 6,610,435

Patent Document 1: U.S. Patent Laid-Open No. 2005/0142414

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, the binding method using thermal pressure bonding or adhesivesof the polymer electrolyte membrane has the possibility of bringingabout deterioration in the performance of the polymer electrolytemembrane caused by heat and the volatile components of the adhesives andis therefore limited in its condition. Further, the binding method usinga mechanical cramp gives rise to the problem that the cross-leak from afine clearance between the polymer electrolyte membrane and the frameeasily occurs.

In the structure of the electrode-membrane-frame assembly as shown inFIG. 16, since the structure is adopted in which the second gasket 308is arranged which prevents the clearance 303 from being created betweenthe inside periphery of the frame 300 and the electrode 302, there is aproblem that this method requires a high production cost. Furthermore,this method has the problem of difficult dimensional control whenfilling the clearance by partially melting this gasket 308.

Further, in the structure of the electrode-membrane-frame assembly ofPatent Document 1, a part of the inside periphery of the gasket is inpartly contact with the outside periphery of the electrode 302 andtherefore, the effect of suppressing the cross-leak phenomenon isinsufficient. Further, the gas diffusion electrode has the problem thatthe electrode is easily damaged in the fabrication because the majorcomponent of the gas diffusion electrode is usually fragile carbonfibers.

Furthermore, none of Patent Documents 2 to 7 discloses such anelectrode-membrane-frame assembly that improves each utilization ratioof reductant gas and oxidizer gas while efficiently suppressing theoccurrence of the cross-leak phenomenon.

Accordingly, it is an object of the present invention to solve the aboveproblem and to provide a polymer electrolyte fuel cell which canefficiently suppress the occurrence of the cross-leak phenomenon inwhich gas leaks through the clearance between the polymer electrolytemembrane and therefore, can more improve the rate of utilization ratioof each of the reductant gas and the oxidizer gas and can be moreimproved in performance of the polymer electrolyte fuel cell, and toprovide a manufacturing method for electrode-membrane-frame assembly tobe used in such a polymer electrolyte fuel cell.

Means for solving the Subject

In order to achieve the above object, the present invention isconstructed as follows.

According to a first aspect of the present invention, there is provideda polymer electrolyte fuel cell assembled by stacking a plurality ofsingle cell modules each comprising an electrode-membrane-frame assemblywhich is formed of a membrane electrode assembly constituted by bindingan anode electrode to one surface of a polymer electrolyte membrane andbinding a cathode electrode to the other surface of the polymerelectrode membrane in such a manner that the periphery of the polymerelectrolyte membrane is exposed, and a frame which contains a gas supplysection that supplies fuel gas and oxidizer gas to the anode electrodeand the cathode electrode respectively and which sandwiches theperiphery of the electrolyte membrane to support the membrane electrodeassembly; and a pair of separators which sandwich theelectrode-membrane-frame assembly from the anode side and the cathodeside,

the electrode-membrane-frame assembly comprising;

an inner elastic member which is arranged on the electrolyte membrane soas to extend along the outer periphery of the electrode between theouter periphery of the anode electrode or cathode electrode and theinner periphery of the frame, the inner elastic member being bound tothe frame;

an outer elastic member which is arranged so as to extend along theinner elastic member between the outer periphery and inner periphery ofthe frame, the outer elastic member being bound to the frame; and

a plurality of connecting elastic members which connect the innerelastic member with the outer elastic member, the connecting elasticmembers being bound to the frame, wherein

the inner elastic member and the outer elastic member respectively havea thickness higher than a dimension of an interval between theelectrode-membrane-frame assembly and the separator after the singlecell module is assembled and in the condition where the single cellmodule is assembled, each of the elastic members is elastically deformedin a direction of a thickness of the electrode-membrane-frame assemblyto hermetically seal the space between the electrode-membrane-frameassembly and the separator.

According to a second aspect of the present invention, there is providedthe polymer electrolyte fuel cell as defined in the first aspect,wherein the inner elastic member is formed over the entire periphery ofthe anode electrode or the cathode electrode except for the formationposition of a gas passage used to supply gas to the anode electrode orthe cathode electrode from the gas supply section of the frame in theelectrode-membrane-frame assembly.

According to a third aspect of the present invention, there is providedthe polymer electrolyte fuel cell as defined in the first aspect,wherein the outer elastic member is formed such that its top is higherthan that of the inner elastic member and the outer elastic memberfunctions as a gasket which hermetically seals the space between themembrane-electrode assembly and the separator out of the single cellmodule.

According to a fourth aspect of the present invention, there is providedthe polymer electrolyte fuel cell as defined in the first aspect,wherein the inner elastic member, the outer elastic member and theconnecting elastic member are each formed on the front side and thebackside of the electrode-membrane-frame assembly.

According to a fifth aspect of the present invention, there is providedthe polymer electrolyte fuel cell as defined in the first aspect,wherein the inner elastic member, the outer elastic member and theconnecting elastic members are each formed as an assembly by injectionmolding and an injection gate trace elastic member formed at a resininjection gate in injection molding is connected only to said outerelastic member among said elastic members.

According to a sixth aspect of the present invention, there is providedthe polymer electrolyte fuel cell as defined in the fifth aspect,wherein the inner elastic member, the outer elastic member and theconnecting elastic member are each formed on a front side or a backsideof the electrode-membrane-frame assembly;

the outer elastic member on the surface side and the outer elasticmember on the backside among the elastic members are connected by theinjection gate trace elastic member; and

a through-hole with said injection gate trace elastic member formedinside thereof is formed in said frame.

According to a seventh aspect of the present invention, there isprovided a manufacturing method for an electrode-membrane-frame assemblyin a polymer electrolyte fuel cell assembled by stacking a plurality ofsingle cell modules each comprising an electrode-membrane-frame assemblywhich is formed of a membrane-electrode assembly constituted by bindingan anode electrode to one surface of a polymer electrolyte membrane andbinding a cathode electrode to the other surface of the polymerelectrolyte membrane in such a manner that the periphery of the polymerelectrolyte membrane is exposed, and a frame which contains a gas supplysection that supplies fuel gas and oxidizer gas to the anode electrodeand the cathode electrode respectively and which sandwiches theperiphery of the electrolyte membrane to support the membrane-electrodeassembly; and a pair of separators which sandwich theelectrode-membrane-frame assembly from the anode side and the cathodeside, the method comprising:

arranging the electrode-membrane-frame assembly in a mold for injectionmolding to form a first flow passage arranged on the electrolytemembrane so as to extend along the outer periphery of the electrodebetween the outer periphery of the anode electrode or the cathodeelectrode and the inner periphery of the frame, a second flow passagearranged so as to extend along the inner elastic member between theinner periphery and outer periphery of the frame and a plurality ofconnecting flow passages which communicate the first flow passage withthe second flow passage in the electrode-membrane-frame assembly;

injecting an elastic resin into the first flow passage to fill the firstflow passage with the elastic resin and to also fill the second flowpassage with the elastic resin through each of the communicating flowpassages; and

curing the filled elastic resin, thereby integrating an elastic memberwhich is elastically deformed in a thickness direction of theelectrode-membrane-frame assembly in each of the first and second flowpassages and in each of the communicating flow passages in the state ofbeing assembled the single cell module to hermetically seal the spacebetween the electrode-membrane-frame assembly and the separator.

According to an eighth aspect of the present invention, there isprovided the manufacturing method for the electrode-membrane-frameassembly as defined in the seventh aspect, wherein the first flowpassage is formed over the entire periphery of the anode electrode orthe cathode electrode except for the formation position of a gas passageused to supply gas to the anode electrode or the cathode electrode fromthe gas supply section of the frame in the electrode-membrane-frameassembly.

According to a ninth aspect of the present invention, there is providedthe manufacturing method for the electrode-membrane-frame assembly asdefined in the seventh aspect, wherein the first and second flowpassages have a depth higher than the dimension of the interval betweenthe electrode-membrane-frame assembly and the separator in the state ofbeing assembled the single cell module.

According to a tenth aspect of the present invention, there is providedthe manufacturing method for the electrode-membrane-frame assembly asdefined in the seventh aspect, wherein, in the formation of the flowpassages, each of the communicating passages is formed so as to have alarger sectional area than the others with an increase in the distancefrom the position at which the elastic resin is injected in the firstflow passage.

According to an eleventh aspect of the present invention, there isprovided the manufacturing method for the electrode-membrane-frameassembly as defined in the seventh aspect, wherein, in the formation ofthe flow passages, the first and second flow passages and each of thecommunicating flow passages are formed on the anode side and cathodeside surfaces of the electrode-membrane-frame assembly, and the elasticresin is simultaneously filled in the first flow passage of the anodeside and the first flow passage of the cathode side through athrough-hole of the frame.

According to a twelfth aspect of the present invention, there isprovided the manufacturing method for the electrode-membrane-frameassembly as defined in the seventh aspect, wherein, in the formation ofthe flow passages, each of the flow passage is formed such that thesectional area of each of the connecting flow passages is smaller thanthat of the first flow passage and that of second flow passage.

According to a thirteenth aspect of the present invention, there isprovided the manufacturing method for the electrode-membrane-frameassembly as defined in the seventh aspect, wherein, in the formation ofthe flow passages, the top of the first passage is higher than that ofthe second passage.

EFFECTS OF THE INVENTION

According to the present invention, the electrode-membrane-frameassembly is provided with an anode side inner elastic member having, forexample, a horizontally frame shape and a cathode side inner elasticmember having a horizontally frame shape on the inner periphery of theframe supporting the polymer electrolyte membrane and the like. Withthis structure, a seal effect can be produced by elastically deformingthe anode side inner elastic member between the frame and the anode sideseparator to bring the elastic member into hermetically contact with theframe and the anode side separator to seal when a unit cell isfabricated. Further, in the same as in the cathode side, a seal effectcan be produced by elastically deforming the cathode side inner elasticmember between the frame and the cathode side separator to bring theelastic member into hermetically contact with the frame and the cathodeside separator to seal when a unit cell is fabricated.

As a result, the cross-leak phenomenon in which gas leaks through theclearance between the polymer electrolyte membrane and the frame can beefficiently suppressed, and each of a short-cut flow of the reductantgas along the periphery of the frame and the short-cut flow of theoxidizer gas along the periphery of the frame can be suppressed. As aresult, each utilization ratio of the reductant gas and the oxidizer gascan be more enhanced to thereby more improve the performance of thepolymer electrolyte fuel cell.

Moreover, the outer elastic member is arranged along the outerperipheral side of this inner elastic member and at the same time, aplurality of connecting elastic members connecting the inner elasticmember with the outer elastic member are formed, thereby making itpossible to form the inner elastic member without fail while preventingthermal damages to the electrode portion or the like even by the resinpressure uniformed by injection molding. Specifically, after a resin isinjected into a first flow passage corresponding to the outer elasticmember to decrease a variation in resin pressure, the resin isintroduced into and filled in a second flow passage corresponding to theinner elastic member through a communicating flow passage correspondingto the connecting elastic member, whereby the resin pressure in thesecond flow passage can be uniformed. Therefore, the resin made to belocally put into a high-pressure and high-temperature state can beprevented from flowing into the second flow passage which is in contactwith the electrode portion or the like, and then the inner elasticmember can be formed without fail.

BRIEF DESCRIPTION OF DRAWINGS

These aspects and features of the present invention will become clearfrom the following description taken in conjunction with the preferredembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic structural view showing the schematic structure ofa fuel cell provided with a fuel cell stack according to a firstembodiment of the present invention.

FIG. 2 is a schematic exploded view of the fuel cell stack with whichthe fuel cell shown in FIG. 1 is provided.

FIG. 3A is a schematic sectional view of a unit cell of the fuel cellstack before the unit cell is assembled.

FIG. 3B is a schematic sectional view of a unit cell after the unit cellis assembled.

FIG. 4 is a schematic partial perspective view of a MEA-frame assembly.

FIG. 5 is a sectional view along the line A-A in the MEA-frame assemblyof FIG. 4.

FIG. 6A is a schematic view showing the procedures for forming anelastic member of the MEA-frame assembly of the first embodiment byinjection molding.

FIG. 6B is a schematic view showing the procedures for forming theelastic member of the MEA-frame assembly of the first embodiment byinjection molding.

FIG. 6C is a schematic view showing the procedures for forming theelastic member of the MEA-frame assembly of the first embodiment byinjection molding.

FIG. 6D is a schematic view showing the procedures for forming theelastic member of the MEA-frame assembly of the first embodiment byinjection molding.

FIG. 6E is a schematic view showing the procedures for forming theelastic member of the MEA-frame assembly of the first embodiment byinjection molding.

FIG. 7 is a schematic view of a unit cell according to a modification ofa first embodiment.

FIG. 8A is a schematic perspective view of a MEA-frame assemblyaccording to a second embodiment of the present invention.

FIG. 8B is a sectional view along the line B-B in the MEA-frame assemblyof FIG. 8A.

FIG. 9 is a schematic perspective view of a MEA-frame assembly accordingto a third embodiment of the present invention.

FIG. 10 is a schematic sectional view of a MEA-frame assembly accordingto a fourth embodiment of the present invention.

FIG. 11 is a schematic sectional view of a MEA-frame assembly accordingto a fifth embodiment of the present invention.

FIG. 12A is a schematic sectional view showing a method for forming anelastic member of a MEA-frame assembly according to a sixth embodimentof the present invention by injection molding.

FIG. 12B is a schematic sectional view showing a method for forming theelastic member of a MEA-frame assembly according to a sixth embodimentby injection molding.

FIG. 13 is a graph showing the results obtained by measuring thedistribution of pressure in a resin flow passage in an embodiment of thepresent invention.

FIG. 14A is a plan view of a frame of a unit cell in the firstembodiment.

FIG. 14B is a front view of the anode side surface of a frame of theabove unit cell of the first embodiment.

FIG. 14C is a front view of the cathode side surface of a frame of theabove unit cell of the first embodiment.

FIG. 15 is an exploded sectional view of an electrode-membrane-frameassembly of an example of a conventional solid polymer electrolyte fuelcell.

FIG. 16 is a sectional view of an electrode-membrane-frame assembly ofan example of a conventional solid polymer electrolyte fuel cell.

BEST MODE FOR CARRYING OUT THE INVENTION

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

Hereinbelow, an embodiment of the present invention will be described indetail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic structural view showing the schematic structure ofa fuel cell provided with a fuel cell stack according to a firstembodiment of the present invention. Further, FIG. 2 is a schematicexploded view of the fuel cell stack (hereinafter referred to as“stack”) with which a fuel cell 101 shown in FIG. 1 is provided.

The fuel cell 101 is, for example, a solid polymer electrolyte fuel cell(PEFC) that generates power, heat and water at the same time byelectrochemically reacting fuel gas containing hydrogen with oxidizergas containing oxygen such as air. As shown in FIG. 1, the fuel cell 101is provided with a stack 30 having a stacked structure in which aplurality of fuel cells (or unit cells) provided with a pair of anodeand cathode are connected in series, a fuel treating unit 31 whichextracts hydrogen from fuel gas, an anode humidifier 32 which humidifiesthe fuel gas containing hydrogen extracted in the fuel treating unit 31to thereby improve power generation efficiency, a cathode humidifier 33which humidifies oxygen-containing gas (oxidizer gas) and pumps 34 and35 that supply the fuel gas and the oxygen-containing gas, respectively.Specifically, the fuel treating unit 31, the anode humidifier 32 and thepump 34 constitutes a fuel supply unit that supplies the fuel gas toeach cell of the gas stack 30. Further, the cathode humidifier 33 andthe pump 35 constitute an oxidizer supply unit that supplies theoxidizer gas to each cell of the stack 30. Here, as such a fuel supplyunit and an oxidizer supply unit, other various structures may beadopted insofar as they have the ability to supply the fuel andoxidizer. In this first embodiment, any supply unit can obtain theeffect of the first embodiment which will be described later as long asit is a supply unit that supplies the fuel and oxidizer to a pluralityof cells with which the stack 30 is provided in common.

Further, the fuel cell 101 is provided with a pump 36 that suppliescooling water to be circulated for efficiently removing the heatgenerated in the stack 30 when power is generated, a heat exchanger 37that exchanges the heat removed by this cooling water (for example, aliquid having no electroconductivity such as pure water is used) with afluid such as city water and a warm-water tank 38 that reserves theheat-exchanged top water. Furthermore, the fuel cell 101 is providedwith an operation control device 40 that performs a control operationfor power generation by correlating the operation with each structuralsection and a power output section 41 that draws the power generated bythe stack 30.

Further, as shown in FIG. 2, the stack 30 mounted on this fuel cell 101is constituted by stacking a plurality of single cells (single cellmodule) 20 which are basic unit structures and by fastening the stackedcells with a current collecting plate 21, an insulating plate 22 and anend plate 23 from both sides under a prescribed load. Each of thecurrent collecting plates 21 is provided with a current drawing terminalpart 21 a, from which current, that is, power is drawn when the power isgenerated. Each insulating plate 22 insulates the current collectingplate 21 from the end plate 23. Further, these insulating plates 22 mayalso be provided with introduction and discharge ports for gas andcooling-water, though not shown, depending on the case. Each end plate23 fastens and supports the a plurality of stacked single cells 20, thecurrent collecting plate 21 and the insulating plate 22 under aprescribed load by a pressure means (though not shown).

As shown in FIG. 2, the single cell 20 is structured in such a mannerthat an electrode-membrane-frame assembly (hereinafter referred to as“MEA-frame assembly”) in which a MEA (membrane-electrode assembly) 1 issupported by a frame is sandwiched between a pair of separators 5 b and5 c.

MEA 1 is structured by forming a catalyst layer (anode side catalystlayer) 112 containing, as its major component, a carbon powder carryinga platinum-ruthenium alloy catalyst on the anode surface side of apolymer electrolyte membrane 1 a that selectively transfers hydrogenions and a catalyst layer (cathode side catalyst layer) 113 containing,as its major component, a carbon powder carrying a platinum catalyst onthe cathode surface side and by arranging a gas diffusion layer 114having both fuel gas or oxidizer gas permeability and electronconductivity on the outside surfaces of these catalyst layers 112 and113. As the polymer electrolyte membrane 1 a, a solid polymer materialexhibiting proton conductivity, for example, a perfluorosulfonic acidmembrane (Nafion membrane, manufactured by Du Pont) is generally used.Here, hereinafter, the anode side catalyst layer 112 and the gasdiffusion layer 114 are collectively called “anode electrode 1 b” andthe cathode side catalyst layer 113 and the gas diffusion layer 114 arecollectively called “cathode electrode 1 c”.

Each of the separators 5 b and 5 c may be made of a gas-impermeableelectroconductive material and for example, those obtained by cutting acarbon material impregnated with a resin into a specified shape or thoseobtained by molding mixtures of a carbon powder and a resin material areusually used. A concave groove is formed on the parts of the separators5 b and 5 c which are in contact with the MEA-frame assembly 15. Whenthis groove is brought into contact with the gas diffusion layer 114, agas flow passage is formed which serves to supply fuel gas or oxidizergas to the electrode surfaces of the anode electrode 1 b and the cathodeelectrode 1 c and to convey excess gas. As the base material of the gasdiffusion layer 114, a material formed of carbon fibers is usually used.As such a base material, for example, a carbon fiber woven fabric isused.

Here, an enlarged schematic partial sectional view of the vicinity(vicinity of the end part of the MEA-frame assembly) of the end part ofthe single cell 20 is shown in FIGS. 3A and 3B.

The single cell (single cell module) 20 is provided with the MEA-frameassembly 15 and the pair of separators 5 b and 5 c that sandwich theMEA-frame assembly 15 from the anode side and the cathode side. TheMEA-frame assembly 15 is constituted of a MEA 1 formed by binding theanode electrode 1 b to one surface of the polymer electrolyte membrane 1a and binding the cathode electrode 1 c to the other surface of theelectrolyte membrane 1 a, and a frame 2 which is provided with gassupply sections 2 x and 2 y for supplying fuel gas and oxidizer gas tothe anode electrode 1 b and cathode electrode 1 c respectively (see FIG.14A) and supports the MEA 1 by sandwiching the peripheral part of thisMEA 1. Then, a plurality of these single cells 20 are stacked to make anassembly, thereby forming a polymer electrolyte fuel cell.

In such a structure, for example, the polymer electrolyte membrane 1 ais mechanically bound by inserting it into a polymer electrolytemembrane insertion slit 2 a of the frame 2 to support it. Further, theanode electrode 1 b and the cathode electrode 1 c are attached andsecured to both surfaces of the polymer electrolyte membrane 1 a.

The anode electrode 1 b and the cathode electrode 1 c are attached andsecured to both surfaces of the polymer electrolyte membrane 1 a to formMEA (membrane-electrode assembly) 1 in this manner and the MEA-frameassembly 15 in which this MEA1 is sandwiched and supported by the frame2 is sandwiched between the pair of separators 5 b and 5 c to form thesingle cell 20. In this single cell 20, the anode electrode sideseparator 5 b is made to be facing the anode electrode 1 b and thecathode electrode side separator 5 c is made to be facing the cathodeelectrode 1 c.

Next, a description will be given as to the structure of the elasticmember formed in the MEA-frame assembly 15. In the MEA-frame assembly 15which is not provided with this elastic body, clearances, for example,ranging from 0.1 mm to 10 mm exist between each of the outer peripheryof the anode electrode 1 b and outer periphery of the cathode electrode1 c, and each of the inner peripheries 2 b and 2 c of the frame 2respectively in the situation where the single cell is fabricated. TheMEA-frame assembly 15 is provided with elastic bodies formed for thepurpose and function of filling the clearances formed along each of theelectrodes 1 b and 1 c and of sealing the clearances between each of theseparators 5 b and 5 c and the frame 2.

Specifically, as shown in FIG. 3A, an anode side inner elastic member 4b is arranged which is extended along the outer periphery of the anodeelectrode 1 b so as to be in contact with both of the anode side innerperiphery 2 b of the frame 2 and the outer periphery of the anodeelectrode 1 b and has a rectangular section. This anode side innerelastic member 4 b is bound with the frame 2 and the anode electrode 1 bto be integrated. Similarly, a cathode side inner elastic member 4 c isdisposed which is extended along the outer periphery of the cathodeelectrode 1 c so as to be in contact with both of the cathode side innerperiphery 2 c of the frame 2 and the outer periphery of the cathodeelectrode 1 c and has a rectangular section. This cathode side innerelastic member 4 c is bound with the frame 2 and the cathode electrode 1c to be integrated. These inner elastic members 4 b and 4 c, in thesituation as shown in FIG. 3A, are in the condition where they arearranged on and only in contact with the polymer electrolyte membrane 1a and there is no need to be adhered. Further, the clearances betweeneach of the outer periphery of the anode electrode 1 b and the outerperiphery of the cathode electrode 1 c and each of the inner peripheries2 b and 2 c of the frame 2 are remarkably reduced by the inner elasticmembers 4 b and 4 c. For example, the inner elastic members 4 b and 4 care formed such that clearances S1 between the inner peripheries of theinner elastic members 4 b and 4 c and each of the outer periphery of theanode electrode 1 b and the outer periphery of the cathode electrode 1 cslightly exist or become 0 (zero).

When the MEA-frame assembly 15 is arranged between the separators 5 band 5 c in the situation where the inner elastic members 4 b and 4 c areformed in this manner to stack, thereby fabricating the single cell 20,the frame built-up surface 9 of the frame 2 is close to the built-upsurface 10 of each of the separators 5 b and 5 c. At this time, eachthickness of the inner elastic members 4 b and 4 c is so designed that aclearance S3 (see FIG. 3A) between the surfaces facing each other, thatis, between the inner elastic member 4 b and 4 c and the separators 5 band 5 c is smaller than a clearance S2 (see FIG. 3A) between the frame 2and each of the separators 5 b and 5 c. When the inner elastic members 4b and 4 c are structured in this manner, the inner elastic members 4 band 4 c are brought into contact with the separators 5 b and 5 crespectively to start elastic deformation without fail before the framebuilt-up surface 9 of the frame 2 is placed at a position closest toeach separator built-up surface 10 of the separators 5 b and 5 c (seeFIG. 3B). Then, after completion of the fabrication, in other words,after the frame built-up surface 9 of the frame 2 is placed at aposition closest to each separator built-up surface 10 of the separators5 b and 5 c, the inner elastic members 4 b and 4 c are pressed by theseparators 5 b and 5 c into an elastically deformed state, respectively,as shown in FIG. 3. As a result, the elastically deformed inner elasticmembers 4 b and 4 c serve to eliminate the clearance S1, so that theclearances existing between each of the outer periphery of the anodeelectrode 1 b and the outer periphery of the cathode 1 c and each of theinner peripheries 2 b and 2 c of the frame 2 respectively are put intosuch a state that they are completely filled with the inner elasticmembers 4 b and 4 c after these parts are fabricated.

Further, as shown in FIG. 3A, an anode side outer elastic member 3 b anda cathode side outer elastic member 3 c are arranged which are extendedalong the inner peripheries 2 b and 2 c of the frame 2 and have arectangular section at a position apart in the outside direction fromthe inner elastic members 4 b and 4 c respectively on the frame built-upsurface 9 of the frame 2. This anode side outer elastic member 3 b isbound to the frame 2 to be integrated. Similarly, the cathode side outerelastic member 3 c is also bound to the frame 2 to be integrated.Moreover, a concave part 10 a is formed on the separator built-upsurface 10 facing the position where each of the outer elastic members 3b and 3 c are formed. The outer elastic members 3 b and 3 c are formedin such a manner as to have a higher rise than the inner elastic members4 b and 4 c on the frame built-up surface 9. Specifically, each top(upper surface) of the outer elastic members 3 b and 3 c is formed suchthat it has a higher height than each top (upper surface) of the innerelastic bodies 4 b and 4 c. Moreover, each thickness of the outerelastic members 3 b and 3 c and the depth of the concave part 10 a ofthe separator built-up surface 10 are so designed that the outer elasticmembers 3 b and 3 c are brought into contact with the bottom of theconcave part 10 a of each of the separators 5 b and 5 c without fail tostart elastic deformation before the frame built-up surface 9 is placedat a position closest to the separator built-up surface 10. Then, afterthe frame built-up surface 9 is placed at the closest position, theouter elastic members 3 b and 3 c are, as shown in FIG. 3B, pressedagainst the inside of the concave part 10 a of the separators 5 b and 5c into an elastically deformed state. As a result, the elasticallydeformed outer elastic members 3 b and 3 c serve to seal the spacebetween the frame built-up surface 9 and the separator built-up surface10 from the outside of the single cell 20.

The structure of the MEA-frame assembly 15 having such an elastic memberwill be described in more detail. Upon describing this, a schematicpartial enlarged view (perspective view) of the vicinity of the end partof the MEA-frame assembly 15 is shown in FIG. 4, and a sectional viewalong the line A-A in FIG. 4 is shown in FIG. 5.

As shown in FIGS. 4 and 5, the inner elastic members 4 b and 4 c areformed on the frame 2 of the MEA-frame assembly 15 in such a manner thatthey are extended along the inner peripheries 2 b and 2 c, respectively.Moreover, on the frame built-up surface 9, the outer elastic bodies 3 band 3 c are formed in such a manner as to be extended in parallel to theinner elastic members 4 b and 4 c at a position apart in the outsidedirection from the inner elastic members 4 b and 4 c. Moreover, aplurality of connecting elastic members 6 b are formed that respectivelyconnect the anode side inner elastic body 4 b with the anode side outerelastic member 3 b at a plurality of positions and have a rectangularsection. Similarly, a plurality of connecting elastic members 6 c areformed that respectively connect the cathode side inner elastic body 4 cwith the cathode side outer elastic member 3 c at a plurality ofpositions and have a rectangular section.

The elastic members 3 b, 3 c, 4 b, 4 c, 6 b and 6 c are each formedintegrally using an elastic resin by injection molding. Agate trace 7formed as a trace of resin injection opening (gate) for injecting aresin in such injection molding is formed in such a manner as to becommunicated only with the outer elastic members 3 b and 3 c.Specifically, as shown in FIGS. 4 and 5, the gate trace 7 is formed soas to communicate the anode side and cathode side frame built-upsurfaces 9 and at the same time, to connect with the anode side outerelastic member 3 b and with the cathode side outer elastic member 3 c byusing a through hole 2 d penetrating through the frame 2.

The above arrangement and connecting structure of the gate trace (gate)7, outer elastic members 3 b and 3 c, connecting elastic members 6 b and6 c and inner elastic members 4 b and 4 c are adopted and an elasticresin injected into the gate corresponding to the gate trace 7 isthereby filled in a flow passage corresponding to the outer elasticmembers 3 b and 3 c and furthermore filled in a flow passagecorresponding to the inner elastic members 4 b and 4 c through the flowpassage corresponding to the connecting elastic members 6 b and 6 crespectively, thereby forming each elastic member in a mold flow passageforming each elastic member. Such a formation method using injectionmolding will be described later.

Here, a schematic plan view of the frame 2 of the MEA-frame assembly 15is shown in FIGS. 14A to 14C. The frame 2 is, as shown in FIGS. 14A to14C, provided with at least a pair of gas supply parts, that is, a fuelgas manifold hole 15 a, an oxidizer gas manifold hole 15 b and a coolingwater manifold hole 15 c. Further, the frame 2 is further provided witha plurality of through-holes 16 for passing a bolt (not shown) thatfastens the single cells 20 one another. Oxidizer gas is supplied to thecathode electrode 1 c side and discharged from the pair of oxidizer gasmanifold holes 15 b of the frame 2. From the pair of fuel gas manifoldholes 15 a of the frame 2, fuel gas is supplied to the anode electrode 1b side and discharged. Further, cooling water is supplied to the spacebetween the backsides of the separators 5 b and 5 c of the neighboringsingle cells 20 which backsides are facing each other and dischargedfrom the pair of cooling water manifold holes 15 c.

The frame 2 is furthermore provided with the outer elastic member 3which functions as a gasket enclosing the whole region which containsthe oxidizer gas manifold hole 15 b and an oxidizer gas flow passage(gas flow passage section) 2 y and where oxidizer gas passes in thecathode electrode 1 c on the frame built-up surface 9 which is thesurface on the side where the cathode electrode 1 c is positioned.Further, the frame 2 is provided with the outer elastic member 3 b whichfunctions as a gasket enclosing the whole region which contains the fuelgas manifold hole 15 a and a fuel gas flow passage (gas flow passagesection) 2 x and where fuel gas passes in the anode electrode 1 b on theframe built-up surface 9 which is the surface on the side where theanode electrode 1 b of the frame 2 is positioned. Further, the outerelastic members 3 b and 3 c are so designed that they are respectivelyisolated from the region where the gas passes and only enclose thecooling water manifold hole 15 c. Accordingly, it is so devised thatafter the single cell is fabricated, the outer elastic members 3 b and 3c are inserted into the concave parts of the separator built-up surfaces10 of the separators 5 b and 5 c and elastically deformed in contactwith that concave parts respectively to thereby prevent the leak of thefuel gas, oxidizer gas and cooling water on the cathode side and theanode side independently. Here, in FIGS. 14A to 14C, the illustrationsof a plurality of connecting elastic members 6 b and 6 c are not given.However, it is preferable that the connecting elastic member 6 c be notarranged in the vicinity of the gas flow passage part 4 c-1 of thecathode side inner elastic member 4 c but be arranged in the vicinity ofits periphery to thereby secure a gas flow passage. Further, the anodeside has the same structure and it is therefore possible to form a spacefor gas supply between the gas flow passage part 4 b-1 of the anode sideinner elastic member 4 b and the anode side separator 5 b without fail.The outer elastic members 3 b and 3 c are continuously formed over thewhole periphery of the frame 2 in this manner and further, the innerelastic members 4 b and 4 c are continuously formed over the entireperiphery of the frame 2 except for the position where the gas supplypassage from the gas supply section is formed.

Further, as the elastic resin material forming these elastic members, itis preferable to use, for example, a thermoplastic elastomer. A specificexample of the elastic resin material includes Milastomer™, highhardness M3800 manufactured by Mitsui Chemicals, Inc. Further, asrequirements for accomplishing elastic deformation of each of theelastic members without fail, any elastic member may be used as long asit has the elasticity of A50 to A90 or D37 to D60 prescribed in JIS K6253.

Specific examples of the material of the frame include R-250G or R-350Gmanufactured by Prime Polymer Co., Ltd. Specific examples of thematerial of the separator include a resin-impregnated graphite plate(glassy carbon manufactured by Tokai Carbon Co., Ltd.) having anexternal dimension of 120 mm×120 mm and a thickness of 3.0 mm.

When the separators 5 b and 5 c are stacked on the MEA-frame assembly 15in the fabrication of the single cell 20, the inner elastic members 4 band 4 c are, as shown in FIG. 3B, compressed and elastically deformed bythe separators 5 b and 5 c, respectively. As a result, the polymerelectrolyte membrane 1 a is pressed along the thickness directionthereof by the compression force of the inner elastic members 4 b and 4c. Therefore, even if the polymer electrolyte membrane 1 a is notattached to the inner elastic members 4 b and 4 c, the inner elasticmembers 4 b and 4 c are brought into close contact with the polymerelectrolyte membrane 1 a by this pressure and the elasticity of theinner elastic members 4 b and 4 c, ensuring that the space between theboth is sealed without fail. Further, the clearance S1 between each ofthe outer periphery of the anode electrode 1 b and the outer peripheryof the cathode electrode 1 c and the inner peripheries 2 b and 2 c ofthe frame 2 can be remarkably reduced, or can be eliminated by elasticdeformation of the inner elastic members 4 b and 4 c between theseparators 5 b and 5 c and frame 2. Specifically, the clearance S1 canbe substantially eliminated.

Therefore, the space between the frame 2 and the anode side separator 5b and the space between the frame 2 and the cathode side separator 5 care respectively sealed hermetically by the anode side inner elasticmember 4 b and the cathode side inner elastic member 4 c which areelastically deformed, making it possible to efficiently prevent thecross leak phenomenon (phenomenon in which cross leak arises) in whichgas passes through the clearance between the polymer electrolytemembrane 1 a and the frame 2. Moreover, the space above the polymerelectrolyte membrane 1 a between the outer periphery of the anodeelectrode 1 b and the inner periphery of the frame 2, and the spaceabove the polymer electrolyte membrane 1 a between the outer peripheryof the cathode electrode 1 c and the inner periphery of the frame 2 arefilled with the elastically deformed inner elastic members 4 b and 4 crespectively. Therefore, the short-cut flow of the reductant gas alongthe inner periphery of the frame 2 and the short-cut flow of theoxidizer gas along the inner periphery of the frame 2 can be prevent,respectively. As a result, each utilization ratio of the reductant gasand the oxidizer gas can be more enhanced, whereby the performance ofthe polymer electrolyte fuel cell can be more improved.

Further, the effect of preventing such a short-cut flow can also beobtained by each of the connecting elastic members 6 b and 6 c.Moreover, the outer elastic members 3 b and 3 c can be made to functionas the conventional gasket.

Next, a method for forming each of the elastic members having suchstructures by injection molding will be described with reference toschematic explanatory views shown in FIGS. 6A to 6E.

First, as shown in FIG. 6A, an upper mold 50 and a lower mold 60 areprepared in which the MEA-frame assembly 15 (MEA-frame assembly in thesituation before the elastic members are formed) in the state that theMEA 1 and the frame 2 are integrated is arranged. In the lower mold 60,the MEA-frame assembly 15 is arranged on its upper surface and at thesame time, a flow passage formation surface 61 which is a concavity andconvexity part for forming a prescribed flow passage between the lowermold 60 and the lower surface of the MEA-frame assembly 15 is formed.The lower mold 60 is furthermore provided with a bar-like raising member62 that separates the MEA-frame assembly 15 together with the moldedresin from the flow passage formation surface 61. The upper mold 50covers the upper surface of the MEA-frame assembly 15 with the lowersurface thereof and at the same time, is also formed with a flow passageformation surface 51 which is an concavity and convexity part forforming a prescribed flow passage between itself and the upper surfaceof the MEA-frame assembly 15. Moreover, a plurality of gates 52 whichare resin injection openings are formed on this flow passage formationsurface 51 and each gate 52 is communicated with a resin introductionsection 53 which is a concave part formed on the upper surface of theupper mold 50. Further, the upper mold 50 is provided with a clampingmember 54 that clamps the upper mold 50 and the lower mold 60 in thecondition where the both molds are aligned. Here, as shown in FIG. 6A, athrough hole 2 d is formed in advance in the frame 2 of the MEA-frameassembly at a position corresponding to each gate 52.

Next, as shown in FIG. 6B, the MEA-frame assembly 15 is mounted on theflow passage formation surface 61 of the lower mold 60. After that, asshown in FIG. 6C, the upper mold 50 and the lower mold 60 mounted withthe MEA-frame assembly 15 are clamped by the clamping member 54. In thesituation where the both molds are clamped, a flow passage in which aresin is allowed to flow and to be filled is formed between each of theflow passage formation surfaces 51 and 61 and the MEA-frame assembly 15.

Specifically, a first resin flow passage 65 corresponding to the anodeside outer elastic member 3 b, a second resin flow passage 66corresponding to the inner elastic member 4 b and a plurality ofcommunicating resin passages 67 (flow passages corresponding to theconnecting elastic member 6 b) that communicates the first resin flowpassage 65 with the second resin flow passage 66 are formed between thepassage formation surface 61 of the lower mold 60 and the MEA-frameassembly 15. Further, a first resin flow passage 55 corresponding to thecathode side outer elastic member 3 c, a second resin flow passagecorresponding to the inner elastic member 4 c and a plurality ofcommunicating resin passages 57 (flow passages corresponding to theconnecting elastic member 6 c) that communicates the first resin flowpassage 55 with the second resin flow passage 56 are formed between theflow passage formation surface 51 of the upper mold 50 and the MEA-frameassembly 15. Here, as is also clear from FIG. 6 c, the first resin flowpassages 55 and 65 and the second resin flow passages 56 and 66 areformed into a horizontally frame form along the frame 2.

Next, as shown in FIG. 6D, an elastic resin is ejected and injected intothe mold. Specifically, the ejected and injected elastic resin P in theresin introduction section 53 of the upper mold 50 is first injectedinto the first resin flow passage 55 formed on the upper mold 50 sidethrough each gate 52 and at the same time, injected into the first resinflow passage 65 formed on the lower mold 60 side through eachthrough-hole 2 d of the frame 2. Next, the resin injected into each ofthe first resin flow passages 55 and 56 is flowed into each of thesecond resin flow passages 56 and 66 through the communicating resinflow passages 57 and 67, respectively. The resin is filled in eachpassage by such a flow of the resin.

Since the resin is first injected into the first resin flow passages 55and 65 from the gate 52, a variation in pressure when the resin isinjected is absorbed to thereby reduce the dispersion of resin pressureat each position in the flow passage. In other words, the pressure ofthe resin can be uniformed. Furthermore, the resin is made to flow intothe second resin flow passages 55 and 66 from the first resin flowpassages 55 and 56 through the communicating resin flow passages 57 and67 respectively, whereby the pressure can be furthermore made uniform.Further, the resin is allowed to pass through each of the communicatingresin flow passages 57 and 67 and filled in the second resin flowpassages 56 and 66 from the first resin flow passages 55 and 55, wherebythe dispersion of filling time (resin arrival time) at each position inthe second resin flow passages 56 and 66 can be reduced. In other words,the dispersion of temperature of the resin at a position can be reduced,making it possible to uniform the temperature of the resin.Particularly, in injection molding in this manner, a high-temperatureand high-pressure resin is to be injected, however, a resin decreased inthe dispersion of temperature is introduced under uniformed pressureinto the junction between the electrode portion which is a part relativelower in thermal strength and the frame 2, and it is therefore possibleto form an elastic member by injection molding while preventing thejunction from being damaged.

When the filling of the resin in all flow passages is completed, theresin is cured. After that, as shown in FIG. 6E, the clamping forceapplied to the upper mold 50 and the lower mold 60 is released and theMEA-frame assembly 15 provided with elastic members formed at positionscorresponding to the passages is released from the flow passageformation surface 61 of the lower mold 60 by the raising member 62.Here, the injection molding is completed.

As a result of the completion of this injection molding, as shown inFIG. 4, the anode side outer elastic member 3 b is formed at a positioncorresponding to the first resin flow passage 65, the inner elasticmember 4 b is formed at a position corresponding to the second resinflow passage 66 and the connecting elastic member 6 b is formed at aposition corresponding to each communicating resin flow passage 67 inthe MEA-frame assembly 15. Further, in the MEA-frame assembly 15, thecathode side outer elastic member 3 c is formed at a positioncorresponding to the first resin flow passage 55, the inner elasticmember 4 c is formed at a position corresponding to the second resinflow passage 56 and the connecting elastic member 6 c is formed at aposition corresponding to each communicating resin flow passage 57.Further, the gate trace 7 is formed at a position corresponding to thegate 52 and through-hole 2 d.

Here, a description of the preferable shape and arrangement of eachelastic member for attaining the resin pressure uniformity and the resinarrival time uniformity in injection molding in this manner is givenwith reference to FIG. 4.

First, the dimension d1 of each thickness of the outer elastic members 3b and 3 c is designed to be preferably in a range from 0.5 mm to 4.0 mm.Further, the sectional area of the member is designed to be preferablyin a range from 1 mm² to 20 mm². If the dimension of the thickness orthe sectional area is excessively smaller than the above range, theouter elastic member dose not function as a resin buffer for making thepressure uniform, whereas if the dimension is excessively larger thanthe above range, the resin material becomes useless.

The formation interval d2 of the gate trace (gate) 7 is preferably in arange from 20 to 100 mm. This is because if the interval is low, theresin material becomes useless whereas if the interval is wide, it isdifficult to make the pressure uniform.

The dimension d3 of each width of the connecting elastic members 6 b and6 c is designed to be preferably in a range from 0.5 mm to 3.0 mm andthe dimension d4 of each thickness is designed to be preferably 0.5 mmto 3.0 mm. In the case where the dimensions are smaller than the aboverange, pressure loss in the flow of the resin is large, therefore it isdifficult to obtain uniform pressure. Further, if the sectional area ofthe connecting elastic members 6 b and 6 c is not made to be smallerthan at least the sectional area of the outer elastic members 3 b and 3c, it is difficult to obtain the effect of pressure uniformity. Here,each sectional area of the connecting elastic members 6 b and 6 c ispreferably designed to be about 5 to 70% based on each sectional area ofthe outer elastic members 3 b and 3 c. Moreover, the formation ofinterval pitch d5 of the connecting elastic members 6 b and 6 c ispreferably designed to be in a range from 3.0 mm to 20 mm. When thepitch is less than the above range, it is difficult to manufacture theconnecting elastic members, whereas if the pitch exceeds the aboverange, the effect of pressure uniformity is decreased.

The relation between the dimension d3 of each width of the connectingelastic members 6 b and 6 c and the interval dimension d6 (intervaldimension d6=formation interval pitch d5−width dimension d3) of each ofthe neighboring connecting elastic members 6 b and 6 c preferablysatisfies: d3/d6≦1. If the requirements of such relation are made to besatisfied, the frame 2 can sufficiently stand to the resin-fillingpressure when the elastic member is formed.

In the above descriptions of this embodiment, the case where each of theouter elastic members 3 b and 3 c and the inner elastic members 4 b and4 c has a rectangular section is described, however, this embodiment isnot limited only to such a case. For example, the case where, like theMEA-frame assembly 75 according to a modification shown by the schematicperspective view of FIG. 7, inner elastic members 74 b and 74 c eachhaving a sectional shape with a slant surface and outer elastic members73 b and 73 c each having a sectional shape with a smooth rise curvatureare formed may be adopted instead of the above case. With such astructure, a MEA-frame assembly can be provided which is superior inhermetically sealing property and is resistant to damages or the likewhile suppressing the amount of the resin to be used. Here, in theMEA-frame assembly 75 shown in FIG. 7, a plurality of connecting elasticmembers 76 b are also formed that connect the outer elastic members 73 band 73 c with the inner elastic members 74 b and 74 c respectively.

Second Embodiment

Here, the present invention is not limited to the above embodiment andmay be practiced in other various embodiments. For example, FIG. 8Ashows a schematic partial perspective view of a MEA-frame assembly 85with which a fuel cell is provided according to a second embodiment ofthe present invention and FIG. 8B shows a sectional view along the lineB-B of FIG. 8A. Here, in the following descriptions, the same structuralmembers as those of the MEA-frame assembly of the above first embodimentare designated as the same reference numbers and the descriptions ofthese members are not given.

As shown in FIGS. 8A and 8B, the MEA-frame assembly 85 of this secondembodiment is different from that of the first embodiment in theposition of the gate which is the resin injection opening used to formeach elastic member by injection molding. Specifically, a gate trace 87is provided on the upper surface in illustration of the cathode sideouter elastic member 3 c. Moreover, a through-hole 2 d is formed so asto penetrate through the frame 2 at a position just under illustrationof the gate trace 87.

According to such a structure of the MEA-frame assembly 85 of thissecond embodiment, the position of the gate is set to the upper surfaceof the outer elastic member 3 c and therefore, the region on the framebuilt-up surface 9 can be utilized efficiently.

Third Embodiment

Next, a schematic partial perspective view of a MEA-frame assembly 95with which a fuel cell is provided according to a third embodiment ofthe present invention is shown in FIG. 9. As shown in FIG. 9, theMEA-frame assembly 95 of this third embodiment is furthermore differentfrom those of the above first and second embodiments in the position ofthe gate which is the resin injection opening in the injection molding.Specifically, a gate trace 97 is arranged in the space between theconnecting elastic members 6 c between the cathode side outer elasticmember 3 c and the inner elastic member 4 c. Here, a through-hole 2 d isformed so as to penetrate through the frame 2 at a position just underillustration of the gate trace 97.

According to the structure of the MEA-frame assembly 95 of this thirdembodiment, the gate is positioned between the outer elastic member 3 cand the inner elastic member 4 c and therefore, the space between theelastic members can be utilized efficiently, leading to efficient use ofthe area on the frame built-up surface 9. Further, unlike the abovesecond embodiment, the gate trace 87 is not formed on the upper surfaceof the outer elastic member 3 c, and therefore, the hermetically sealingfunction of the outer elastic member 3 c, that is, the function as agasket for the outer elastic member 3 c and the separator 5 c is nothindered and hermetic sealing can be accomplished without fail.

Fourth Embodiment

Next, a schematic partial sectional view of a MEA-frame assembly 115with which a fuel cell is provided according to a fourth embodiment ofthe present invention is shown in FIG. 10. As shown in FIG. 10, theMEA-frame assembly 115 of this fourth embodiment is different from thatof each of the above embodiments in the point that it is furthermoreprovided with intermediate elastic members 118 b and 118 c arranged soas to extend along each elastic member between the outer elastic members3 b and 3 c and the inner elastic members 4 b and 4 c. Furthermore, theintermediate elastic members 118 b and 118 c are connected with theouter elastic members 3 b and 3 c by a plurality of connecting members119 b and 119 c, respectively. Further, the intermediate elastic members118 b and 118 c are connected with the inner elastic member 4 b and 4 cby a plurality of connecting members 6 b and 6 c, respectively.

In the structure of the MEA-frame assembly 115 of such third embodiment,the function as the resin buffer for making pressure uniform in theresin flow passage corresponding to the outer elastic member is achievedin a process divided into two stages using the resin flow passagescorresponding to the outer elastic member and to the intermediateelastic member. Furthermore, the resin passes through the resin flowpassages corresponding to at least two connecting resin membersresultantly by the time when it reaches the resin passage correspondingto the inner elastic member. Therefore, the effect of the resin pressureuniformity and the arrival time of the resin flowed into the flowpassage corresponding to the inner elastic member can be more enhanced.

Fifth Embodiment

Next, a schematic partial perspective view of a MEA-frame assembly 125with which a fuel cell is provided according to a fifth embodiment ofthe present invention is shown in FIG. 11. As shown in FIG. 11, theMEA-frame assembly 125 of this fifth embodiment is different from thatof each of the above embodiments in the point that each of theconnecting elastic members 126 a, 126 b and 126 c is formed so as tohave a larger sectional area than others in proportion to the distancefrom the gate trace (gate) 7. Specifically, in FIG. 11, each sectionalarea is designed so that the sectional area of the connecting elasticmember 126 a arranged at a position closest to the gate trace 7 issmallest, then, the connecting elastic member 126 b has a largersectional area and the connecting elastic member 126 c has the largestsectional area, in this order.

Since each of the connecting elastic members 126 a, 126 b and 126 c isdesigned to have a larger sectional area than others in proportion tothe distance from the gate trace (gate) 7, pressure loss in the flow ofthe resin from the gate into the flow passage corresponding to the innerelastic member can be made uniform, thereby making it possible toenhance the effect of the resin pressure uniformity.

Sixth Embodiment

Next, a method for producing a MEA-frame assembly with which a fuel cellis provided according to a six embodiment of the present invention willbe described with reference to schematic explanatory views of FIGS. 12Aand 12B.

In each of the above embodiments, the case where the elastic members areformed integrally simultaneously on each surface of the anode side andthe cathode side of the MEA-frame assembly by injection molding isdescribed. However, the present invention is not only limited to such acase. Specifically, as shown in FIG. 12A, an elastic resin is injectedfrom the gate 7 c by injection molding on one surface, for example,cathode side surface 9 a, of the MEA-frame assembly 135 to thereby formthe cathode side outer elastic member 133 c, each of the connectingelastic members 136 c and the inner elastic member 134 c. Thereafter, asshown in FIG. 12B, an elastic resin is newly injected from the gate 7 bby injection molding on the other surface, for example, anode sidesurface 9 b, of the MEA-frame assembly to thereby form the anode sideouter elastic member 133 b, each of the connecting elastic members 136 band the inner elastic member 134 b.

In this manner, the elastic members can be formed separately on eachsurface of the MEA-frame assembly 135 by injection molding. Further,this formation method has an advantage that it is unnecessary to form athrough-hole in the frame 2.

Here, in each of the above embodiments, the case where the elasticmember is formed on each of the anode side and cathode side surfaces ofthe MEA-frame assembly is described as an example. However, the presentinvention may also be the case where the elastic member is formed ononly one surface of the MEA-frame assembly 15, instead of the abovecase. Even in the case where the elastic member is arranged on only onesurface, the effect of suppressing the cross-leak of gas can beobtained.

Working Example

Here, the graph of FIG. 13 shows the results obtained by measuring thedistribution of pressure of the elastic resin in the second resin flowpassage corresponding to the inner elastic member in the MEA-frameassembly 15 having the structure of the above first embodiment (WorkingExample) and the distribution of pressure in the resin flow passageprovided with no connecting resin flow passage as the resin flow passageof the MEA-frame assembly according to Comparative Example.

In the graph showing the distribution of pressure in FIG. 13, theordinate is the pressure (MPa) of the resin and the abscissa is thepositions of measuring points. Here, the measuring point 22 is placed ata position closest to the gate which is the resin injection opening andmeasuring points closer to the measuring point 1 or measuring point 41are more distant from the gate.

In the MEA-frame assembly of Comparative Example provided with nocommunicating resin flow passage, as shown in FIG. 13, the pressure ofthe resin reaches about 5 MPa at the measuring point 22. On the otherhand, in the case of forming the communicating resin flow passagesimilar to the MEA-frame assembly 14 of Working Example, the upper limitof the pressure of the resin can be suppressed to about 2.9 MPa or lessand it is found that the effect of the pressure uniformity is obtained.

Therefore, the structure of the MEA-frame assembly of each of the aboveembodiments ensures that the resin pressure uniformity in the flowpassage and the time uniformity required to fill the resin into the flowpassage can be made, and it is possible to form the inner elastic memberby injection molding which suppresses the occurrence of cross-leak toachieve hermetic sealing at the junction between the electrode portionwhich is relatively reduced in thermal strength and the frame.

It is to be noted that, by properly combining the arbitrary embodimentsof the aforementioned various embodiments, the effects possessed by themcan be produced.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

The entire disclosure of Japanese Patent Application No. 2007-091975filed on Mar. 30, 2007, including specification, drawings and claims forpatent, are incorporated herein by reference in its entirety.

1. A polymer electrolyte fuel cell assembled by stacking a plurality ofsingle cell modules, each of the single cell modules comprising: apolymer membrane electrode; an anode electrode and a cathode electrodeformed on both surfaces of the membrane electrode; a frame whichsandwiches a part of the electrolyte membrane; a pair of separatorswhich sandwich the anode electrode and the cathode electrode; an innerelastic member which is arranged on the inner periphery of the frame soas to extend along the outer periphery of the electrodes, each of theelectrodes being formed at the inner side of the frame; outer elasticmembers which are arranged so as to extend along the inner elasticmember on both of separator-side surfaces of the frame on which theseparators are placed; and a plurality of connecting elastic memberswhich are arranged on the frame and which connect the inner elasticmember with the outer elastic members, wherein the inner elastic memberis more protruding than the separator-side surface of the frame, andeach of the outer elastic members is placed so as to face a concave partwhich is formed on each of the separators, and in the assembled state,the inner elastic member and the outer elastic members are elasticallydeformed thereby sealing a space between the separators, and theelectrodes, the membrane electrode and the frame.
 2. The polymerelectrolyte fuel cell as defined in claim 1, further comprising: a pumpfor supplying cooling water to be circulated into the fuel cell; a heatexchanger for exchanging the heat removed by the cooling water with afluid; and a warm-water tank for reserving the heat-exchanged fluid. 3.The polymer electrolyte fuel cell as defined in claim 2, furthercomprising: an operation control device for performing a controloperation for the fuel cell; and a power output unit for drawing thepower generated by the fuel cell.